Preheat the oven to 400F. Line a large baking sheet with parchment paper. Place the butter in the freezer for 10 minutes so it gets extra cold.
In a large bowl, mix together the flour, salt, baking powder, baking soda, and brown sugar.
In a smaller bowl, whisk the egg. Add the blended cottage cheese, lemon juice, and lemon zest, and mix until combined.
Add the wet mixture to the dry ingredients and mix gently until just combined.
Take the butter out of the freezer and grate it into the dough, kneading lightly as you go so it disperses evenly.
Gently fold in the blueberries, being careful not to overmix or crush them. If the dough is too dry and blueberries are hard to fold in, add more lemon juice or water.
Form the dough into a ball and roll it on a floured surface into an 8-inch circle. Cut into 8 triangles and carefully transfer to the prepared baking sheet.
Prepare the egg wash by whisking the egg with water. Brush the tops of the scones with the egg wash.
Bake for 18–20 minutes, until lightly golden. Remove from the oven and let the scones cool on the baking sheet.
Optional: Mix the lemon juice with powdered sugar to make the glaze and drizzle over the scones before serving.